The present invention relates to a device for detecting respective tires with reduced air pressure on a vehicle. More specifically, the present invention relates to a tire deflation warning system which reliably carries out the judgment of tires with reduced air pressure when the air pressures of the all wheels are simultaneously reduced.
The air pressures of tires are gradually lowered even if tires are not damaged. Simultaneous reduced pressures occasionally occur because air permeates the rubber of tires in addition to the dimension growth of new tires and the simultaneous reduced pressure caused by the lowering of atmospheric temperature. It happens to be dangerous that a vehicle runs while being in reduced pressure, and since fuel cost is deteriorated, influence to environment is also concerned.
Accordingly, there have been proposed methods for detecting simultaneous deflation of 4 wheels in addition to the detection of deflation of one wheel.
For example, there is a method for detecting the simultaneous deflation of 4 wheels utilizing the difference of load sensitivity, from the inclination of relation between the judging value (DEL value) of reduced pressure by the difference of sum of 2 pairs of the rotational speeds of wheels which are situated at diagonal to a vehicle and acceleration to a lateral direction (lateral G), and from the value of a yaw rate sensor and the rotational speed ratio of left and right wheels.
For example, additionally, there is a method for detecting the simultaneous deflation of 2 driving wheels utilizing the change of frictional coefficient—slipping coefficient (μ-s) property (Japanese Unexamined Patent Publication No. 17717/2004, Japanese Unexamined Patent Publication No. 291616/2003, Japanese Unexamined Patent Publication No. 326927/2003 and Japanese Unexamined Patent Publication No. 267012/2003). The method for utilizing the (μ-s) property can also detect the simultaneous deflation of 4 wheels. Additionally, there is a method for enabling the detection of the deflation of 2 wheels at the same axis by comparing the rotational speed ratio of the front and rear wheels, with the rotational speed ratio of the front and rear wheels at normal air pressure, in running state in which a vehicle has no driving force (Japanese Unexamined Patent Publication No. 220811/2003), and a method for detecting the simultaneous deflation of 4 wheels.